A typical diaper construction comprises an absorbent pad or batt or the like enclosed in an outer plastic shell or a non-woven backsheet. The backsheet is typically a non-woven fabric laminated with a water impermeable layer such as a polyethylene film. A water permeable inner shell or liner is also provided to promote separation of fluid from the user.
Typical diapers include a fastener system usually in the form of a tape. The fastener tape system generally includes adhesive tabs fastened to one end of the diaper assembly construction at each lateral side of the diaper in a permanent “factory joint” by the diaper manufacturer using adhesives or other techniques. The tabs typically have a face coated with pressure sensitive adhesive. The tabs are releasably attachable to the other end of the diaper to allow unfastening to inspect the diaper in a nonpermanent “user joint” followed by refastening if indicated.
The user joint may be formed by direct connection of the tab to the diaper outer surface whether the outer surface is formed of a plastic film or a non-woven backsheet. In the case of plastic film shells, it is typical to provide a “landing zone” for the tab to form the user joint. The landing zone may provide a plastic surface of a non-woven surface and may comprise a knit type fabric landing pad.
Securing a fastener to a diaper at the factory joint is typically performed so as to provide a strong and durable affixment. Several techniques have been used including mechanical bonding procedures and the use of high strength adhesives.
A recent trend in diaper construction is the use of increasingly softer materials. This is typically achieved by utilizing nonwoven materials having relatively high degrees of loft. Although no standard definition of loft exists, typically, high loft nonwovens have relatively low densities. The term “high loft” when referring to nonwoven materials typically refers to any fiber structure containing more air than fiber. Regardless of a precise definition, it is difficult to form a factory joint by bonding a fastener such as a tape fastener to a high loft nonwoven material. This is believed to be due to the difficulty in contacting the adhesive face of the fastener with a sufficient number of fibers in the nonwoven material. Due to the high loft of certain nonwoven materials, a significant proportion of the fibers reside relatively far underneath the outer surface of the nonwoven. Thus, in forming a factory joint and in order to reach the fibers residing well under the nonwoven outer surface, relatively high lamination forces must be applied between the adhesive face of the fastener and the nonwoven.
Furthermore, many adhesives that are used to bond fasteners with a nonwoven material to form a factory joint are formulated to have a relatively high internal strength. A consequence of this is that the adhesives are relatively hard and resistant to flow. Accordingly, during formation of a factory joint, very high lamination forces must be used in order for the adhesive to sufficiently flow and thereby bond with the fibers of the nonwoven.
Increasing lamination force typically increases demands on manufacturing equipment and power requirements. Moreover, if the new required lamination forces are sufficiently high, process equipment may need to be modified or entirely replaced with larger equipment. As will be appreciated, modifying or replacing equipment is costly and undesirable. In addition, high lamination forces may also damage the fastener or components of the fastener. For example, if the fastener includes one or more regions of mechanical fasteners such as hook and loop type fasteners, damage to the hook members can occur. Specifically, after the fastener has been attached to a diaper and folded or placed in a stored position, if high lamination forces are applied to the fastener, the hook members and potentially also the loop members can become deformed or distorted. Such damage typically results in nonfunctionality of the mechanical fasteners. Furthermore, high lamination forces may also detrimentally impact conversion speeds. Accordingly, a need exists for a strategy by which fasteners can be securely adhered to high loft nonwoven materials, while avoiding the use of relatively high lamination forces. In addition, a need exists for a technique by which relatively hard adhesives can be securely adhered to nonwovens and particularly, to high loft nonwoven materials, while avoiding the use of relatively high lamination forces.
Reducing costs is a concern in nearly every diaper manufacturing process. Since most processes are high volume, even relatively small reductions in cost per unit can result in significant savings when large numbers of units are produced. Although many cost efficient processes are known for diaper manufacturing, a need remains for further strategies and techniques for reducing costs associated with diapers and related fastening systems.